1. Field of the Invention
The present invention relates to a semiconductor memory device and a manufacturing method thereof.
2. Description of the Related Art
A phase-change memory (PCM), such as a phase-change random access memory (PCRAM), can be of high storage density and high endurance, and can be written and/or read with high speed and driven with low drive current.
FIG. 1 illustrates a diagram illustrating a memory cell 100 of a PCRAM device having a buried electrode contact (BEC). As shown in FIG. 1, the memory cell 100 has a first insulating layer 107 in which a lower via, a BEC, is formed, wherein the lower via contacts a first electrode 101 and comprises a liner 103 and a metal plug 105. For example, the liner 103 can be formed of titanium nitride (TiN), while the metal plug 105 embedded in the liner 103 can be formed of one or more of copper, aluminium, tungsten, nickel and/or one or more of other metals, an alloy of some of these metals, or a stack of some of these metals. The lower via contacts a phase-change material layer 113 (which may be a phase-change material island or phase-change material island-shaped layer) that is formed in a second insulating layer 109; the lower via serves as an electrode for the phase-change material layer 113. A second electrode 115 is provided on the phase-change material layer 113 and can be a contact or a via, for example. A third insulating layer 111 is formed to cover the second electrode 115.
A small electrode contact area in a PCRAM device is critical for reducing the drive current and device size.
As indicated by the double-arrow line in FIG. 1, the BEC (i.e., the lower via) has a critical dimension (width or diameter) of about 70 nm. Given existing standard contact processes, it is difficult to directly form a BEC with a 70 nm critical dimension using a patterning process at the 180 nm or 130 nm process node. On the other hand, an advanced process capable of patterning 70 nm critical dimensions may substantially increase the process cost and/or the equipment cost.